File.delete one-liner

[David Stanford]

Hi guys,

I'm looking for a single line that essentially deletes the lockfile
argument passed to the unlock method, or deletes the instance variable
(default) lockfile. Like this, but simpler:

@lockfile = some_other_lockfile

def self.unlock(lockfile)
if File.exist?(lockfile)
File.delete(lockfile)
else
File.delete(@lockfile)
end
end


I was thinking of something along the following:

@lockfile = some_other_lockfile

def self.unlock
File.delete(lockfile) || File.delete(@lockfile)
end

...however, the File.delete method doesn't return a true/false value
based on its success.

Any tips? Thanks in advance!

-David

 

[Joel VanderWerf]

Hi guys,

I'm looking for a single line that essentially deletes the lockfile
argument passed to the unlock method, or deletes the instance variable
(default) lockfile. Like this, but simpler:

@lockfile = some_other_lockfile

def self.unlock(lockfile)
if File.exist?(lockfile)
File.delete(lockfile)
else
File.delete(@lockfile)
end
end


I was thinking of something along the following:

@lockfile = some_other_lockfile

def self.unlock
File.delete(lockfile) || File.delete(@lockfile)
end

...however, the File.delete method doesn't return a true/false value
based on its success.

Any tips? Thanks in advance!

-David

Use exceptions?

begin
File.delete(lf)
rescue Errno::ENOENT
File.delete(@lf)
end

 

[David Stanford]

Use exceptions?

begin
File.delete(lf)
rescue Errno::ENOENT
File.delete(@lf)
end

Thanks Joel. Forgive me, I'm just learning Ruby/scripting/programming. I
believe I understand your example, but (as far as I can tell) it doesn't
really accomplish my goal, and seems to have the same functionality of
my first (longer) example.

Please let me know if I've missed something.

In any case, I think I found a (seemingly) obvious solution to my
question:

@lockfile = some_other_lockfile

def self.unlock(lockfile)
File.exist?(lockfile) ? File.delete(lockfile) : File.delete(@lockfile)
end


Thanks again!

-David

 

[Joel VanderWerf]

Thanks Joel. Forgive me, I'm just learning Ruby/scripting/programming. I
believe I understand your example, but (as far as I can tell) it doesn't
really accomplish my goal, and seems to have the same functionality of
my first (longer) example.

Please let me know if I've missed something.

In any case, I think I found a (seemingly) obvious solution to my
question:

@lockfile = some_other_lockfile

def self.unlock(lockfile)
File.exist?(lockfile) ? File.delete(lockfile) : File.delete(@lockfile)
end

With exceptions, you are saying "try to delete lf; if that fails
(because the file doesn't exist) then try to delete @lf". Other failures
(e.g., lf permissions are wrong, or @lf doesn't exist) are reported
normally as exceptions.

One advantage to doing it this way is that the delete is an atomic
operation. With

File.exist?(lockfile) ? File.delete(lockfile) : File.delete(@lockfile)

there is the possiblity that #exist? will return true, but in the brief
time before #delete is called, some other process deletes the file.

Btw, it looks to me like your #unlock implementation above is the same
as your first implementation. The ? : construct is really the same as
if...else, just more compact.

 

[Julian Leviston]

File.delete(File.exists?(lockfile) ? lockfile : @lockfile)

Blog: http://random8.zenunit.com/
Learn rails: http://sensei.zenunit.com/

 

[Robert Klemme]

File.delete(File.exists?(lockfile) ? lockfile : @lockfile)

[lockfile, @lockfile].any? {|f| File.delete(f) rescue false}

Cheers

robert

 

[Joel VanderWerf]

File.delete(File.exists?(lockfile) ? lockfile : @lockfile)

[lockfile, @lockfile].any? {|f| File.delete(f) rescue false}

If #delete fails on lockfile for some reason other than ENOENT, this
code will try to delete @lockfile.

 

[Robert Klemme]

File.delete(File.exists?(lockfile) ? lockfile : @lockfile)

[lockfile, @lockfile].any? {|f| File.delete(f) rescue false}

If #delete fails on lockfile for some reason other than ENOENT, this
code will try to delete @lockfile.

This is correct. I thought that was intended. Didn't you suggest
exactly this in your previous posting (atomic deletion)? Looking at the
original question it is not clear in which cases @lockfile should be
deleted - unless you take the code as spec.

Thanks for pointing this out!

Cheers

robert

 

[Joel VanderWerf]

2009/2/4 Julian Leviston <[email protected]>:
File.delete(File.exists?(lockfile) ? lockfile : @lockfile)
[lockfile, @lockfile].any? {|f| File.delete(f) rescue false}

If #delete fails on lockfile for some reason other than ENOENT, this
code will try to delete @lockfile.

This is correct. I thought that was intended. Didn't you suggest
exactly this in your previous posting (atomic deletion)? Looking at the
original question it is not clear in which cases @lockfile should be
deleted - unless you take the code as spec.

Thanks for pointing this out!

The only difference in my suggestion was to "Rescue Errno::ENOENT",
which seems closer to the original intent of using #exists?...

begin
File.delete(lf)
rescue Errno::ENOENT
File.delete(@lf)
end